Risk Factors for Measles Non-Immunity in Previously Immunized Pregnant Patients

Measles immunity testing, unlike that for rubella, is not currently part of routine prenatal screening even though immunity to both is conferred by the measles-mumps-rubella (MMR) vaccine. Although endemic transmission of measles was declared eliminated in the U.S. in 2001 after widespread MMR vaccination programs, outbreaks have continued to occur. The MMR vaccine was a single dose regimen prior to 1989, leading to a potentially under-vaccinated cohort of pregnant individuals who were born before recommendations for a second dose to bolster MMR efficacy. Given the risks associated with measles infection during pregnancy, we sought to identify risk factors for measles non-immunity in rubella-immune pregnant individuals.